Combine textures into one - For Tabletop Simulator
If anyone has an automated way of compositing them I would love to hear about it my self, but so far as I know the unfortunate answer is it has to be done manually.  The way I've always had to do it is to open the three separate textures together as layers in a photoshop type program (I typically use gimp) and arrange them as different squares on a bigger single image.  If at all possible i would make the canvas exactly twice the size of the origonal images and arrange the tiles on there with out resizing as that will help with the next step a little.  after that you have to open the model back up in blender and resize/move around the normal map so they line up with the textures on the new single composite image.  If everything went smoothly this is just a matter of selecting them all scaling to .5 and moving them around as a group till it lines up about right.  if each of the three images was a different size however, which often happens, it can get a bit more fiddly resizing and placing.
P.S.  One thing I forgot to add since you mentioned parts not having color.  the color slider in tts will only change the color to the first &quot;material&quot; the object mentions which can be handy if you want to only have say the base or a specific item of clothing on a character to change color.  so in blender which ever material is at the top of the list will be the one affected.  In the sample pic below I want the scales to be able to be set different colors so I have material.004 which is the scale pattern set at the top of the list